Thermal spray powder incorporating a particular high temperature polymer

ABSTRACT

Powders of oxidized polyarylene sulfide and powders comprising from 1 to 99% by weight of oxidized polyarylene sulfide and from 1 to 99% by weight of a metal, carbide, ceramic or high temperature polyimide, polyamide imide, polyester imide and aromatic polyester plastic, or a mixture thereof are very suitable for use in thermal spraying and thereby form coatings having a strong chemical and mechanical resistance and high dimensional stability when exposed to high and low temperatures. Such coatings are advantageous for use as abradable seal clearance control coating in the compressor section of gas turbine engines, motor vehicle turbochargers and superchargers, and for use as a coating of reaction vessels, kitchen ware, sealings or bearings.

[0001] The invention relates to a material used for thermal sprayingmade from, or preferably, incorporating a particular high temperaturepolymer, and to a process of forming a coating from such material bythermal spraying.

[0002] Thermal spraying is a generic term describing establishedengineering processes whereby a material is formed into a coating byprojecting particles in a stream of hot gases onto a surface. Theinvention relates primarily to thermal spray processes in which thematerial to be deposited is in powder form, but it also includes thermalspray processes where the material to be deposited is in the form of arod or strand, or fabricated structure comprising for example a tubefilled with compacted powder, or any other form in which it can be fedinto thermal spray equipment. The invention relates to all types ofthermal spray processes including the following specific examples:

[0003] Plasma flame spraying including

[0004] Conventional plasma spraying in natural atmosphere known asAtmosphere Plasma Spraying (APS);

[0005] Plasma spraying in a controlled atmosphere such as an inert gas,known as Controlled Atmosphere Plasma Spraying (CAPS), this includes butis not limited to the atmosphere being controlled by enclosing theprocess in a chamber containing the desired gas or gas combination, orby flooding the plasma stream by the desired gas or gas combination;

[0006] Plasma spraying in a partial or complete vacuum known as VacuumPlasma Spraying (VPS).

[0007] Combustion thermal spray processes including

[0008] A conventional combustion flame, normally resulting from thecombustion of a fuel gas such as acetylene in the presence of oxygen.

[0009] A high velocity stream of hot gases resulting from the combustionof a fuel, which may be gaseous or liquid, in the presence of oxygen andthe expansion of the hot gasses being controlled and channelled throughan exit nozzle. This process is well known and recognised by thedescription, high velocity oxy fuel (HVOF);

[0010] A process as described above but the combustion is supported byair instead of oxygen and is known and recognised by the descriptionhigh velocity oxy air (HVAF).

[0011] And Electric arc thermal spray processes where the heat source isderived from an electric arc struck between a cathode and anode whereeither or both may comprise the material being sprayed.

[0012] Powders for thermal spraying typically comprise metals and/orcarbides and/or ceramics although they can also comprise hightemperature polymers and mixtures of high temperature polymers andmetals to which the British patent specification GB 1 356 017 refers. Inparticular, GB 1 356 017 discloses high temperature polyimide, polyamideimide, polyester imide and aromatic polyester plastics suitable forflame spraying processes. Although these high temperature polymers, inparticular aromatic polyester plastics, are used in a number oftechnically important applications, their physical properties, e.g. theresistance against corrosion through salt containing steam, are limited.

[0013] So far, oxidized polyarylene sulfides are used as additives toother polymers such as fluorocarbon polymers (EP-A-0 633 290 and EP-A-0633 291) where they act as fillers, or they are processed into molded orfunctional parts for applications where resistance to high temperaturesis required (EP-B-0 623 639 and EP-A-0 623 640).

[0014] It has now surprisingly been discovered that oxidized polyarylenesulfides are very suitable for use in thermal spraying and thereby formcoatings having a strong chemical and mechanical resistance and highdimensional stability when exposed to high and low temperatures.

[0015] The invention provides a thermal spray powder comprising from 1to 99% by weight, preferably from 5 to 60% by weight, and particularpreferably from 20 to 45% by weight of oxidized polyarylene sulfide andfrom 1 to 99% by weight, preferably from 40 to 95% by weight, andparticular preferably from 55 to 80% by weight of a metal powder.

[0016] The invention also provides a process of forming a thermal spraypowder comprising or essentially consisting of oxidized polyarylenesulfide into a coating by thermal spraying, and a coating produced froma thermal spray powder comprising or essentially consisting of oxidizedpolyarylene sulfide.

[0017] Thermal spray powders comprising oxidized polyarylene sulfideexhibit improved flow and trickle properties compared withconventionally used thermal spray powders comprising high temperaturepolymers. This enhanced property is particularly important for theprocessing of the powder by thermal spraying.

[0018] Further, coatings obtained by thermal spraying powders comprisingoxidized polyarylene sulfide are extremely resistant against corrosionthrough hot and salt containing steam.

[0019] Polymers which can be used for the thermal spray powder accordingto the invention are linear and branched polyarylenes whose recurringunits contain at least one SO₂ or SO group as bridge and which have aheat resistance which is adequate for the thermal spraying applicationsand processing. Favourable polyarylenes have the formula (I)

—[(Ar¹)_(d)—X]_(e)—[(Ar²)_(i)-Y]_(j)—[(Ar³)_(k)-Z]_(l)—[(Ar⁴)_(o)—W]_(p)—  (I)

[0020] in which each Ar¹, Ar², Ar³, Ar⁴, W, X, Y and Z, independently ofthe others, is identical to or different from the others. The indices d,e, i, j, k, l, o and p are, independently of one another, zero orintegers 1, 2, 3, or 4, where at least one of the indices d, i, k and oand at least one of the indices e, j, l and p must be 1. Ar¹, Ar²,Ar³and Ar⁴ in the formula (I) are simple or directly para-, meta- orortho-linked arylene systems having 6 to 18 carbon atoms, W, X, Y and Zare linking groups selected from —SO₂—, —SO—, —CO—, —COO—, alkylene oralkylidene groups, each having 1-6 carbon atoms, and —NR₁—groups whereR₁ is an alkyl or alkylidene group having 1-6 carbon atoms, with theproviso that at least one of the linking groups W. X, Y and Z informular (I) is —SO— or —SO₂—.

[0021] Particularly suitable polymers are polyarylenes containingrecurring units of the formula (II)

[0022] [—(S—E)_(a)—(SO—E)_(b)—(SO₂—E)_(c)—]  (II)

[0023] in which each E, independently of the others, is phenylene,naphthylene or biphenylene, b and c, independently of one another, havevalues of from 0 to 1 and a has values of from 0 to less than 1, withthe proviso that the sum a+b+c is equal to 1 and at least one of theindices is greater than zero and if any sulfur links (—S—) are present,at least further —SO₂— or —SO— links are also present.

[0024] Particularly preferred oxidized polyarylene sulfides are linearor branched polyarylene sulfones, polyarylene sulfide sulfones,polyarylene sulfoxide sulfones, or polyarylene sulfide sulfoxidesulfones.

[0025] Polymers which can be specifically employed are those containingrecurring units of formulae (III)-(VI)

[0026] and oxidized polyphenylene sulfides containing recurring units ofthe formula (VII)

[0027] where the degree of oxidation is at least 50% based on 100% ofthe theoretically possible uptake of oxygen (100% sulfone groups).

[0028] The oxidized polyarylene sulfides can be prepared by theprocesses described in German patent applications: DE 43 14 738, DE 4314 737, DE 43 14 736, DE 43 14 735, DE 44 40 010, P 195 31 163.9, DE 19636 692.5, DE 196 37 845.1, DE 197 16 016 and DE 197 51 239.9, which areexpressly incorporated herein by way of reference.

[0029] Subsequent references in this specification to “the polymer” inthe singular includes reference to each and all of the oxidizedpolyarylene sulfides described above.

[0030] In principle, the polymer can be used for thermal sprayingwithout adding any further components and/or additives. Thermal sprayedcoatings of the polymer itself reflect the basic desirablecharacteristics of the material, including dimensional stability at hightemperature, high adhesion to metals, dielectric strength and highresistance to chemical corrosion. Compared with coatings obtained fromthe polymer through other coating processes, a coating obtained bythermal spraying has greater adhesion onto a surface.

[0031] However, the characteristics can be further improved byincreasing the strength and cohesiveness of the coating therebyimproving the resistance to erosion. Also the resistance to thermalcycling can be improved. These improvements are achieved by the additionof a second component, for example by addition of metals, carbides,ceramics and other high temperature polymers like polyimides, polyamideimides, polyester imides or aromatic polyester plastics, or mixturesthereof. Preferably, these improvements are achieved by the addition ofmetals. A metal addition to the polymer also enhances the bonding of anysubsequent metal layers on the thermal sprayed coating. Further, thermalspray powders comprising the polymer and such second component, inparticular if particles made up of the second component are blended orcoated with the polymer, exhibit improved flow and trickle properties.

[0032] It is also possible to add conventional additives and fillers,for example stabilizers, color pigments, mineral fibers, in particularglass or carbon fibers, and the like to the thermal spray powder. Theonly requirement to such additives and fillers is that they remainstable in the thermal spraying process.

[0033] The thermal spray powder generally comprises from 1 to 99% byweight, preferably from 5 to 60% by weight, and particular preferablyfrom 20 to 45% by weight of the polymer. The share of any othercomponent, in particular of a metal, ceramic, other high temperaturepolymer, mineral filler or mixtures thereof, is from 1 to 99% by weight,preferably from 40 to 95% by weight, and particular preferably from 55to 80% by weight of the thermal spray powder.

[0034] In the case of metal additions, the proportion of the polymer ispreferably of from 5 to 60% by weight of the thermal spray powder, andduring the thermal spray process the metal particles are heated to atemperature close to their melting point and the polymer particles aresurface heat softened. Propelling the heated particles, or mixture ofparticles onto a surface results in the formation of a coating. Typicalmetals for mixing with the polymer are aluminum, alloys of aluminum,copper, bronze, babbit, nickel alloys, stainless steels and alloys ofcobalt/nickel/chrome/aluminum/yttrium (the latter well known by thegeneric term “MCrAlYs”). Since the density of the metal will besignificantly greater than that of the polymer the weight percentage ofpolymer for a given mixture will be less than the volume percentage.

[0035] Materials which perform as solid lubricants, including but notlimited to molybdenum disulphide, calcium fluoride, bentonite, mullite,graphite or boron nitride, can also be added to the thermal spraypowder. Often such materials will be used in combination with metals andthe polymer.

[0036] In accordance with the invention the polymer (normally in powderform) is deposited into a coating by thermal spraying, or preferably isfirst mixed with any other component in powder form to form either aphysical mixture, a composite powder, or combination thereof, and isthen deposited into a coating by thermal spraying.

[0037] If the powder is in the form of composite particles, thecomposite particles can comprise for example relatively large particlesof the polymer coated with relatively fine particles of the addedmaterial, or alternatively for example relatively large particles of theadded material coated with relatively fine particles of the polymer. Thebonding of the polymer and added material to form the compositeparticles may be purely the result of physically blending or tumblingthe components together, or may be enhanced by the addition of a bindingagent, i.e. a resin designed for bonding together dissimilar materialsincluding but not limited to phenolic resins, and/or by the applicationof heat and/or by mechanical loading such as attrition milling or by anyother means.

[0038] In such examples the relatively large particles will be of a sizerange typical of thermal sprayed powders, for example between 20 and 150μm, the relatively fine particles will for example be in the size rangeof from 0.5 to 40 μm. The composite particles may also be of aconstruction whereby for example both the added powder and the polymerpowder are in a very fine powder form having a particle size of from 0.5to 20 μm. In such an example the aggregated particles comprise subparticles of each constituent and may be formed or agglomerated byconventional powder metallurgy techniques with or without a binder or bya spray drying method. Particles formed in these ways may be furtherprocessed to homogenise or densify them. This can be done for example bypassing the agglomerated composite powder through a heat source such asa plasma flame.

[0039] In practice, the thermal spray powder may comprise a powder wherethe components are combined partially as a physical blend and partiallyas a composite. In some cases, one or more of the added materials may bepartly composed of irregular particles and the balance composed ofspherical particles.

[0040] The spraying of the powder mixture in accordance with theinvention is effected by the conventional well known manner for thermalspraying, utilising conventional thermal spray equipment. The thermalspray conditions however must be arranged and controlled to provide forsubstantial melting of the added powder while at the same time heatsoftening the polymer powder. Various factors, including, spray gungeometry and efficiency, flame temperature, gas/particle relativevelocity, thermal properties, size and density of the particle and dwelltime will determine the temperature the particles are heated to.

[0041] In the case of metal additions the greater thermal conductivityof the metal particles will cause them to be more rapidly heated thanthe polymer and consequently they may reach their melting point in thesame environment and under the same conditions that the polymerparticles are only surface heat softened. The term “surface heatsoftened” means a thermal conditioning of the polymer particles in whichthe surface of the polymer is heated to a temperature at which the samewill deform and flow under pressure or impact as is required in thermalspraying. This takes place without heating the entire particle to adetrimental or degrading temperature. Such surface heat softening mayinclude a superficial chemical or physical modification of the polymerpowder surface.

[0042] The spraying may be effected for example by thermal spraying orby any technique whereby the powder is heated and propelled onto asurface to form a coating. In, for example, a plasma flame sprayingprocess the powder may be injected axially or radially, internally orexternally, upstream or downstream of the electric arc. One particularexample of such equipment and associated spray parameters is the MetcoType 9M Plasma Spray System, utilising a 9MB gun and a GP nozzle, No 2powder port, argon plasma forming gas with equipment flow setting of190, with hydrogen added at an equipment flow setting of 5, 75 arc voltsand 500 amperes arc current. Powder is fed to the gun with a Metco Type4 MP powder feeder using argon carrier gas with equipment flow settingof 50 and a powder feed rate of 23 to 26 g/min. Spray distance set at 75mm to 100 mm. Further examples of suitable plasma guns are the MetcoType 3MB, Type 3MB2 and Type 7MB; the Sulzer Metco Type F4; theMetallisation PS50; the SNMI PS2, PS2 EV, and PS4 A; the METTECH Axial3; and the Miller Thermal Model 3702 and Model SG-100.

[0043] Another thermal spray process for example is HVOF. One particularexample of such equipment and associated spray parameters is the MetcoDiamond Jet Series 1000, utilising a V4 Air Cap; V3 Snooted Insert; V3Injector; VA Shell; V4 Siphon Plug; Type B powder feed pick up shaft;Oxygen pressure 11.04 bar equipment flow setting of 40; Propane pressure4.83 bar, equipment flow setting of 40; Nitrogen carrier gas at pressure9.66 bar equipment flow setting of 70; air pressure 5.17 bar equipmentflow setting of 60; spray rate 151 g/min. Spray distance set at 250 mm.Further examples of suitable HVOF guns or systems are the Miller ThermalModel HV-2000; the OSU Super Jet System and Carbide Jet System; theEutectic Taffa model JP-5000, the Eutectic TeroJet.

[0044] Examples of other thermal spray processes are HVAF andconventional combustion flame powder guns such as the Metallisation Mark74, Metco Type 5P and Type 6P Guns; the Eutectic Castolin CastoDyn DS8000 and CDS 8000 Guns; and Colmonoy Guns.

[0045] If the polymer, or polymer in combination with another material,or polymer in combination with metal were to be in the form of a strand,or for example a fabrication comprising powder compacted into a tubethen examples of suitable thermal spray equipment would be the MetcoType 14E; the Metallisation Mark 73, Mark 61 and Mark 66E pistols; theSNMI Master-Jet 2 range; the OSU Type D 8.

[0046] Spraying may be effected on any surface or substrate such ascarbon steel, stainless steel, aluminium and alloys of aluminium, copperand alloys of copper, nickel and alloys of nickel, cobalt alloys,titanium and alloys of titanium. Although the substrate materialnormally comprises metals, other materials may be used including forexample, plastics, oxide ceramics and fibre reinforced compositematerials. The surface is normally cleaned and roughened to achievebonding of the coating. In the case of metal substrates roughening ofthe surface may be achieved by grit blasting. This is an establishedprocess whereby hard sharp edged particles are impacted onto the surfacenormally propelled by high pressure air.

[0047] The sharp edged particles may include chilled cast iron grit ofsize G24, and aluminium oxide of size range between 200 and 800 μm. Thesurface roughness achieved may be in the range from 2 to 6 μm aa.

[0048] Instead of, or preferably as well as surface roughening, asuitable self bonding material may be applied by thermal spraying. Inthe case of metal substrate materials self bonding coating materials arewell known in the thermal spray art, they include molybdenum and variouscomposites and alloys of nickel and aluminium, in wire, fabricated wireand powder form. These materials self bond to most metal substrates.Suitable materials for bonding to other substrates may also be used,such as copper or glass for ceramic substrates. Polymers including theoxidized polyarylene sulfide may be mixed with metals for bonding on tolow melting point substrates, including plastics and fibre reinforcedcomposite materials. In each example the bond coat would be applied in athickness relevant to the material combination in question, for examplenickel aluminium bond coats sprayed on to metal substrates wouldnormally be about 125 μm thick. The polymer/metal mixture is sprayed toa thickness required by the particular application, normally in therange from 0.2 to 8 mm or even more. Depending upon the applicationrequirements the coating will be either used in the as sprayed conditionor there will be a machining operation to provide a suitable dimensionand/or surface finish.

[0049] Coatings produced with a polymer/metal mixture are excellent foruse as abradable seal clearance control coatings up to temperatureslimited by the polymer, typically in the range up to 350° C. or 400° C.for example in the compressor section of gas turbine engines andinternal combustion engine turbochargers and superchargers. Coatingsproduced with the polymer in combination with a high temperature alloy,sometimes also in combination with a solid lubricant, are excellent foruse as adradable seal clearance control coatings at elevated temperatureassociated with the turbine section of a gas turbine engine. In thistype of application, the polymer will disappear at elevated temperatureand is used as a means of producing a thermal sprayed coating ofcontrolled porosity. The same principle can be applied to any type ofdevice or application requiring clearance control by means of anabradable coating. The coatings are also excellent for reaction vessels,heat resistant surfaces of kitchen ware, e.g. for pans, pots or ovens,and for any application where a high chemical and/or temperatureresistance is required. Coatings can also be used for sealing, inparticular on the seal areas of engine and pump shafts, and forbearings, in particular as low friction bearing surfaces. The propertiesof the coatings can under certain circumstances be further modified andadjusted by subsequent processing steps, for example a heat treatment todensify the coating.

[0050] Thermal sprayed layers comprising the polymer and/or the polymerin combination with other materials provide an excellent means forbonding dissimilar materials. Such a layer can be used to enhance thebonding of a wide range of non metallic coatings onto metal components,for example as an intermediate layer to enhance the bonding ofpolytetrafluorethylene (PTFE) onto metal to form a durable non stickcooking surface. Conversely, such a layer can also be used to enhancethe bonding of a wide range of metallic coatings onto non metallicmaterials.

[0051] The following examples are given by way of illustration and notlimitation.

EXAMPLES Preparation of polyphenylene sulfone (PPSO₂)

[0052] 63 kg of polyphenylene sulfide powder (d50: 60 μm) with a Tg of94° C. and a Tm of 290° C. were placed in 219 1 of glacial acetic acidat 50° C., 1.21 of concentrated sulfuric acid were added, and 91 kg ofhydrogen peroxide (50%) were added dropwise over the course of 3 h,during which the temperature rose to 60-65° C. Following anafterstirring time of 2 h at 65° C. and 1 h at 80° C., the reactiondispersion was cooled and filtered off with suction at 50° C., and thesolid product was washed with water and dried.

[0053] Yield: 70 kg; DSC data: Tg: 352° C.; Tm: 520° C. (decomposition)Elemental analysis: (C₆H₄SO₂)n; C: 55.6%, H: 3.2%, S: 24.6%, 0:16.0%.This corresponds to a degree of sulfur oxidation in the polymer of about65%, based on 100% of the theoretically possible uptake of oxygen.

[0054] This polyphenylene sulfone is “the polymer” referred to in thesubsequent examples.

Example 1

[0055] 40% by weight of the polymer in powder form having a size rangeof from 18 to 135 μm and 60% by weight of a silicon aluminium alloy inpowder form containing 12% silicon and having a particle size of from 10to 62 μm were blended together in a tumbling action provided by a coneblender. The resulting mixture comprises composite particles where eachdiscrete particle is made up of both constituents and individualparticles comprising exclusively each constituent. The mixture wassprayed with a Metco Type 9M plasma spray system incorporating a 9MB gunand a 4MP powder feed unit. The 9MB gun was fitted with a GP nozzle, No2 powder port, argon plasma forming gas with equipment flow setting of185, with hydrogen added at an equipment flow setting of 5; the arc wasset at a current of 500 amperes and approximately 75 arc volts. Powderwas fed to the gun with a Metco Type 4 MP powder feeder using argoncarrier gas at an equipment flow setting of 50 and a powder feed rate of23 to 26 g/min. The substrate was a 300 mm length of 150 mm diametertube of mild steel with a wall thickness of 2.4 mm. The substrate wasgrit blasted on the outside diameter with aluminium oxide grit understandard conditions. The substrate was mounted on a turntable androtated, the plasma gun was mounted on a vertical traverse unitconnected to the turntable unit such that the plasma gun traversed upand down with the spray stream impacting normal to the substrate. A bondcoat of 95% nickel and 5% aluminium composite material was appliedutilising standard conditions and sprayed to a thickness of 125 μm. Thepowder mix was then sprayed to a thickness of 1.8 mm utilising a spraydistance of approximately 90 mm.

Example 1-A

[0056] Example 1 was repeated exactly except using a polymer powder witha size range of from 36 to 135 μm.

Example 2

[0057] Example 1 was repeated except for spraying the powder mixture theMetco Type 9M plasma spray system incorporating a 9MB gun wassubstituted by a Sulzer Metco Plasma Technique A2000 system with an F4Torch fitted with a 6mm nozzle, 2.0 mm injector; the spray parametersare changed accordingly to the following, argon plasma gas at a flow of70 liters per min, with hydrogen added at a flow of 8 liters per min;500 amperes arc current; powder was fed to the torch at a rate of 50g/min in a carrier gas flow of 8.5 liters per min. The spray distancewas set at 120 mm.

Example 2-A

[0058] Example 2 was repeated exactly except using a polymer powder witha size range of from 36 to 135 μm.

Example 3

[0059] Example 1 was repeated exactly except the powder mixture wassprayed using a Metco Diamond Jet Series 1000 HVOF spray system insteadof the Metco Type 9M plasma spray system. The Metco Diamond Jet Series1000, utilises a V4 Air Cap; V3 Snooted Insert; V3 Injector; VA Shell;V4 Siphon Plug; Type B powder feed pick up shaft; Oxygen pressure 11.04bar equipment flow setting of 40; Propane pressure 4.83 bar, equipmentflow setting of 40; Nitrogen carrier gas at pressure 9.66 bar equipmentflow setting of 70; air pressure 5.17 bar equipment flow setting of 60;spray rate 150 gm per minute. The spray distance was set at 250 mm.

Example 3-A

[0060] Example 3 was repeated exactly except using a polymer powder witha size range of from 36 to 135 μm.

Example 4

[0061] Examples 1, 2 and 3 were repeated exactly except using differentmixtures comprising a nominal 20%, 25%, 30%, 35%, 45% and 50% by weightof the polymer and in each case the balance of the mix comprising the12% silicon aluminium alloy.

Example 4-A

[0062] Example 4 was repeated exactly except using a polymer powder witha size range of from 36 to 135 μm.

Example 5

[0063] Examples 1, 1-A, 2, 2-A, 3, 3-A, 4 and 4-A were repeatedutilising a 12% silicon aluminum powder which comprises partly powder ofan irregular particle form and of a particle size from 10 to 62 μm (asdescribed in Example 1) and the balance comprising a powder of sphericalparticle form also in the size range from 1 0 to 62 μm.

Example 6

[0064] Examples 1, 1-A, 2, 2-A, 3, 3-A, 4, 4-A and 5 were repeated butthe component powders were mixed or tumbled together in a piece ofequipment such as a cone blender having facility to heat the powdermixture to any predetermined temperature in the range up to 300° C.

Example 6-A

[0065] Example 6 was repeated with the addition of relatively heavybodies, such as stainless steel balls of 1 cm diameter, to providemechanical impact during the tumbling process.

Example 7

[0066] Previous examples were repeated but the silicon-aluminium wasreplaced by an MCrAlY comprising cobalt/nickel/chrome/aluminum/yttriumalloy or cobalt/chrome/aluminum,/yttrium alloy ornickel/chrome/aluminum/yttrium alloy. The thermal and othercharacteristics of such alloys differ from those of silicon-aluminium,consequently the thermal spray parameters are adjusted accordingly. Thepolymer proportion in such a mixture is normally in the range from 5 to40% by weight.

EXAMPLE 7A

[0067] Example 7 was repeated with the addition of one or more materialsin powder form which act as a solid lubricant, for example with graphiteand boron nitride, respectively.

EXAMPLE 8

[0068] A composite powder was produced comprising 40% by weight of thepolymer having a size range of from 18 to 135 μm and 60% by weight of asilicon aluminium alloy containing 12% silicon flake powder having aparticle size below 20 μm. The powders were mixed together withKetjenflex MH a thermoplastic resin supplied by Akzo Nobel ChemicalsLtd. as a binding agent. The components were mixed together in aplanetary mixing device with facility for application of heat to supportcuring of the resin. The resulting powder comprises polymer particlescoated with silicon aluminium together with a small proportion of noncombined component powders. The composite powder was thermal sprayed bythe plasma process as described in Examples 1, 2 and 3.

Example 8-A

[0069] Example 8 was repeated exactly except using a polymer powder witha size range of from 36 to 135 μm.

Example 8-B

[0070] Examples 8 and 8-A were repeated except using different mixturescomprising a nominal 20%, 25%, 30%, 35%, 45% and 50% by weight of thepolymer, in each case the balance of the mixture comprising the 12%silicon aluminium alloy flake 1 5 powder.

Example 8-C

[0071] Examples 8 and 8-A were repeated but replacing the siliconaluminium flake powder with an MCrAlY as described in Example 7.

Example 8-D

[0072] Example 8-C was repeated except using different proportions ofpolymer powder in the range 5% to 40% by weight. Optionally, suchmixtures included a third component to act as a solid lubricant of thetype described in Example 7-A.

Example 9

[0073] Examples 1 and 1-A were repeated but substituting stainless steelpowder for the silicon aluminium powder. The stainless steel was aproprietary alloy with high corrosion resistance to combat theparticular service conditions in which the resulting coating willoperate. Mixes were produced utilising a nominal 5%, 10%, 20%, and 30%by weight of the polymer. The powder mixture was thermal sprayed by theplasma process as described in Examples 1, and 2, or by HVOF asdescribed in Example 3. Thermal spray parameters were tailored to suitthe material properties and coating requirements.

Example 9-A

[0074] Powder mixtures were prepared and sprayed similar to thosedescribed in Example 9 except substituting the stainless steel withaluminum, aluminium bronze, other aluminum alloys, nickel, nickelalloys, copper, copper based alloys and babbitt.

[0075] Through all the Examples 1 to 9-A suitable thermal spray powdersand thermal sprayed coatings showing good adhesion to the surface ontowhich they were sprayed were obtained.

1. A thermal spray powder comprising from 1 to 99% by weight of oxidizedpolyarylene sulfide and from 1 to 99% by weight of a second componentselected from metals, carbides, ceramics and high temperaturepolyimides, polyamide imides, polyester imides and aromatic polyesterplastics, or a mixture thereof.
 2. The powder according to claim 1,comprising from 5 to 60% by weight of oxidized polyarylene sulfide andfrom 40 to 95% by weight of the second component.
 3. The powderaccording to claim 1, wherein the oxidized polyarylene sulfide is apolymer having recurring units of the formula (I)—[(Ar¹)_(d)—X]_(e)—[(Ar²)_(i)—Y]_(j)—[(Ar³)_(k)-Z]_(l)—[(Ar⁴)_(o)—W]_(p)—  (I)in which each Ar¹, Ar², Ar³, Ar⁴, W, X, Y and Z, independently of theothers, is identical to or different from the others; the indices d, e,i, j, k, l, o and p are, independently of one another, zero or integers1, 2, 3, or 4, at least one of the indices d, i, k and o and at leastone of the indices e, j, l and p being 1; Ar¹, Ar², Ar³ and Ar⁴ aresimple or directly para-, meta- or ortho-linked arylene systems havingfrom 6 to 18 carbon atoms; W, X, Y and Z are selected from —SO₂—, —S—,—SO—, —CO—, —COO—, alkylene or alkylidene groups, each having from 1 to6 carbon atoms, and —NR₁—, groups where R₁ is an alkyl or alkylidenegroup having from 1 to 6 carbon atoms, with the proviso that at leastone of the groups W, X, Y and Z is —SO— or —SO₂—.
 4. The powderaccording to claim 1 wherein the oxidized polyarylene sulfide and thesecond component form a composite powder in which discrete particles aremade up of the constituent components.
 5. The powder according to claim4 wherein particles made up of oxidized polyarylene sulfide having aparticle size of from 20 to 150 μm are coated with particles made up ofthe second component having a particle size of from 0.5 to 40 μm and/orparticles made up of the second component having a size of from 20 to150 μm are coated with particles made up of oxidized polyarylene sulfidehaving a size of from 0.5 to 40 μm, or wherein both the particles madeup of oxidized polyarylene sulfide and particles made up of the secondcomponent have a size of from 0.5 to 40 μm.
 6. The powder according toclaim 1 wherein the oxidized polyarylene sulfide and the secondcomponent are partially in the form of a physical mixture and partiallyin the form of a composite powder according to claim 4 or
 5. 7. Thepowder according to claim 4 in which the particles making up the powderare in the form of a rod, a strand or a fabricated structure where apowder is compacted into a tubular sheath.
 8. The powder according toclaim 1 having a particle size of from 10 to 200 μm.
 9. The powderaccording to claim 1 wherein the second component is a metal selectedfrom aluminium, aluminium alloy, copper, bronze, babbitt, nickel, nickelalloy, stainless steel or a mixture thereof.
 10. The powder according toclaim 9 in which the metal is an alloy of silicon and aluminium,containing from 5 to 30% by weight of silicon.
 11. The powder accordingto claim 10 comprising from 58 to 62% by weight of the powder of analuminium alloy containing 12% by weight of silicon.
 12. The powderaccording to claim 1 wherein the second component is an alloy selectedfrom high temperature resistant alloys known generically as an “MCrAlY”.13. The powder according to claim 12 wherein the second component is analloy of cobalt/nickel/chrome/aluminum/yttrium,cobalt/chrome/aluminum/yttrium, or nickel/chrome/aluminum/yttrium, or amixture thereof.
 14. The powder according to claim 12 or 13, furthercomprising a solid self lubricating additive selected from but notnecessarily limited to, molybdenum disulphide, calcium fluoride,bentonite, mullite, graphite and boron nitride.
 15. The powder accordingto claim 14, comprising from 3 to 8% by weight of boron nitride, from 15to 30% by weight of oxidized polyarylene sulfide, and the balance to atotal of 100% by weight of the thermal spray powder of a hightemperature resistant MCrAlY alloy.
 16. A process of forming a powderaccording to any of claims 1 to 15 into a coating by thermal spraying.17. A process of forming a powder according to any of claims 1 to 15into a coating by thermal spraying wherein during thermal spraying thepowder is heated to a temperature sufficient to substantially melt themetal component and heat soften the surface of the polymer component.18. The process according to claim 16 or 17 in which the powderparticles are heated in a plasma or combustion flame, or in a highvelocity oxy fuel (HVOF) or high velocity oxy air (HVAF) combustionflame and deposited by projecting them onto a surface to form a coating.19. The process according to claim 16 or 17 comprising the steps ofthermal spraying and subsequent processing to modify the properties ofthe obtained coating, in particular a process to densify the coating bya heat treatment.
 20. A coating produced by thermal spraying a powderaccording to any of claims 1 to
 15. 21. A coating produced from oxidizedpolyarylene sulfide powder by thermal spraying.
 22. An abradable sealclearance control coating comprising a coating according to claim 20 or21.
 23. An abradable seal clearance control coating according to claim22 in a gas or air compressor or pump.
 24. An abradable seal clearancecontrol coating according to claim 22 or 23 in the compressor section ofgas turbine engines, motor vehicle or other internal combustion engineturbochargers and superchargers.
 25. A coating of on reaction vessels,kitchen ware, sealings or bearings comprising a thermal spray powderaccording to claim 1 or a coating according to claim 20 or 21.